The COMPATIBLE parameter allows us to use the latest Oracle database release, while making sure that the database is compatible with an earlier release.
Suppose we upgrade to the Oracle Database 10g Release 2 version, but our application developers haven’t made any changes to their Oracle9i application. In this case, we could set the COMPATIBLE parameter equal to 9.2 so the untested features of the new Oracle version won’t hurt our application. Later on, after the application has been suitably upgraded, we can reset the COMPATIBLE initialization parameter to 10.2.0, which is the default value for Oracle Database 10g Release 2 (10.2).
If, instead, we immediately raise the compatible value to 10.2, we can use all the new 10.2 features, but we won’t be able to downgrade our database to 9.2 or any other lower versions. We must understand this irreversible compatibility clearly, before we set the value for this parameter.
Default value: 10.2.0
Parameter type: Static